Composite floor of metal and concrete



June 13, 1950 L. coFF I COMPOSITE FLOOR 0F METAL AND CONCRETE 3vSheets-Sheet l Filed Feb. 20, 1946 WITNESSES INVENTOR 72m ma@ June 13,1950 L. coFF 2,510,958

couposm: FLooR oF METAL AND CONCRETE Filed Feb. 2o. 194e :s sheets-sheet2 Fig. 4

w/TNEssEs Y BY W ia i l /NvE/vTo'R June 13', 195o L. COFF 2,510,958

COMPOSITE FLOOR 0F METAL AND CONCRETE Filed Feb. 20, 1946 l 3Sheets-Sheet 3 Fig. 5a

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-wllvEssEs BY @124mg mvENToR Patented June 13, 1950 UNITED STATES PATENTOFFICE COMPOSITE FLOOR OF METAL AND CONCRETE Leo Coil, New York, N. Y.

Application February zo, 1946, seria1No.'s49,o1o In Great Britain July4, 1945 (Cl. 'l2-70) 12 Claims.

The present invention relates toimprovements in the construction ofcomposite structures, and

more particularly to such composite structures away from the concretelayer as the shearing stresses will readily overcome the bond betweenthe two construction elements. This condition is extremely undesirablesince the concrete slab will not bear its proper share oi' the load.

Various remedies have been devised in the form of auxiliary bondingelements, such as spirals, angles, stirrups, and the like, which arewelded to the steel shape and mechanically engage the concrete. Thesedevices are suiilciently effective after the concrete slab has hardened,provided that they have adequate strength to withstand the considerableshear of the loaded structure. The latter requirement tends to increasetheir first cost, particularly since the bonding devices must bedesigned for ample safety margin under maximum load conditions. beingcompletely imbedded in the concrete and therefore not subsequentlyaccessible for inspection, adjustment, or replacement. A furtherdisadvantage is that the steel shape will be prestressed as it sagsunder the weight of the concrete being poured, should conditions make itimpractical to support the structure at intermediate points during thehardening process.

A principal object of the invention is to provide, in a structure of theabove kind, simple and effective means assuring cooperation between theconcrete slab and the metallic support, whereby new forces areintroduced to counteract the shearing stresses; this to such an extentthat the bond between concrete and steel, enhanced by a slight anchoragesuch as roughening (knurling) of the upper ange surface, should sumce toprevent displacement oi the slab relative to its support.

Another object of the invention is to provide shear-controlling meansadjustable to diierent lpeak loads, permitting of prefabrlcation andconvenient on-the-spot adaptation to prevailing conditions.

A further object is to provide shear-controlling means that is readilyaccessible for purposes of reinforcement. replacement, or readjustment.

Still another object is to provide a method o1' manufacturing compositestructures of the kind described whereby prestressing of the supportingshape is avoided, even in cases where it is not feasible to support thesteel member during the hardening process; this to assure cooperation ofthe slab with the beam for dead load as well as live load.

Additional objects will become apparent as the description proceeds withreference to the accompanying drawing, in which several embodiments ofthe invention are illustrated by way of example.

In the drawing- Figs. 1 and 1a show, in longitudinal elevation and incross section respectively, an I-section steel girder according tonormal practice:

Figs. 2 and 2a show, in longitudinal elevation and in end viewrespectively, an embodiment of the invention as applied to such acomposite structure;

Figs. 3 and 3a, in views similar to those of the preceding figures, showa modification;

Figs. 4 and 4a are longitudinal and cross-sectional respectively of aconstruction according to the invention, embodying another modification;

Fig. 5 is an end view of a pair of beams similar to the one of Fig. 2,supporting a common layer of concrete, the structure having beenprestressed according to a method shown in detail in Figs. 7 and 7a;

Fig. 5a is a longitudinal sectional view illustrating a modification ofthe method for prestressing the tension wires before laying theconcrete;

Fig. 6 is a cross-sectional view of a pair of beams supporting a commonlayer of concrete. the structure having been prestressed according toanother modiiication of the method indicated 1n Fis. 5:

Fig. 6a is a fragmentary section along line A-A of Fig. 6;

Figs. 7 and 'Ia show respectively, on a larger scale, an end view and afragmentary side elevation of a beam as illustrated in Fig. 5.

Figures 1 and 1a show a steel or other metal rolled section or girder I,constituting a beam having its ends resting freely on supports S of anykind. 2 indicates a slab or layer of concrete supported by the upperflange 3 of section I. The weight of the concrete layer 2 and anyadditional load thereon will cause a deflection of the structure whichwill progressively increase from the top surface of concrete slab 2 tothe lower surface of section I. Horizontal shear stresses 4 and verticalshear stresses 5 will come into play and by reason of the formerrelative movement will occur between concrete layer 2 and nange 3 inlongitudinal direction oi' shape I. These are the conditions which applyto normal structures comprising concrete slabs supported by metal beamsor girders wherein the bond between the concrete and the metal surfacesis not sufficient to counteract effectively the horizontal shear thatarises.

As already indicated, the main object of the invention is to introducenew forces acting against the horizontal shear stresses. According tothe invention, this result is accomplished by the provision of ametallic tie as illustrated in Figs. 2 and 2a.

We shall assume, for the moment, that the shape I can be supported atintermediate points by shores S' and S". Vertical plates 6a are insertedabove one or more of these points between the two flanges of the shapeand serve as an anchor for a transverse brace, such as the pin 6.Generally, the number of transverse braces 6 will depend on the lengthof the structure. Beneath the pins 6 pass tension' wires 1 of high yieldpoint which are anchored at their ends to angle plates 8 by means ofnuts I1. These nuts can also be used for applying tension to the wires 1before the concrete is laid, thereby lifting the beam I from the shoresS'. If this tension is just sufficient to counterbalance the weight ofthe slab 2, pouring of the concrete will bring the beam I back into itsoriginal position without letting the structure sag after the shores S'have been removed. Loading of the structure will further tension thewire tie 1; this tension has a horizontal component 9, acting upon thelayer 2 through angle plates 8, and a vertical component I0, acting uponthe girder I through pins 6. Whereas the forces 9 will tend to increasethe deflection of the slab 2, forces I will simultaneously limit thedownward movement of the shape I; thus contact between layer 2 andflange 3 will be maintained under varying load conditions.

The wires 1 must be free to slide longitudinally throughout theirlength; if the steel shape I is to be encased in concrete, housings mustbe provided around the pins 8, and the wires either coated or sheathedso that they are not bonded to the concrete.

As an alternative to stressing the wire tie before the concrete ispoured, this may also be done after the dead weight has been applied;tensioning of the wires will then correct the deflection of thecomposite structure. Again the tension may be adjusted to such a valuethat the composite section is deflected upward when not loaded, to anextent equal to the deflection produced by the maximum load expected.Thus the structure receives an initial camber which is wholly or partlyabsorbed by the load. In this case, no break of bond is required betweenthe wires 1 and the concrete encasement, if any, of girder' I, providedthe concrete of such encasement was allowed to harden while maxlmumstress was applied to the wire tie (e. g., by loading the structure).

It is obvious that in the absence of deection there is no shear betweenthe concrete slab and the steel shape; hence the closer We are to thiscondition, the less bond is required in the contact plane for securingfull cooperation. On the other hand, it should be observed that theinitial camberA must not be driven beyond a certain limit, as otherwisethe eilect of the forces 9 will be reversed. Thus, under certain loadconditions, the composite structure of Fig. 2 may be advantageouslyreplaced by the modification shown in Figs. 3 and 3a.

Instead of bearing a slab of uniform thickness, steel shape I in Fig. 3supports a concrete layer II of arched or strongly haunched form. Thewires 1 are anchored to the plates 0a between the rises of adjacentarches II' and II". This construction allows the use of shallowergirders I for the same over-all depth, since deflection can beaccurately regulated by the tension of the tie 1. Moreover it enablesthe anchorages 8a for that tie to be disposed at a more convenient levelas compared with the angle plates 8 of Fig. 2, a fact that results inadditional leeway in the distribution of deflectioncontrolling forces. Afurther advantage is that stressing of the concrete layer throughtensioning of the wires need not impart compression to the steel shape,which may be important especially when the latter is not encased.

It will be appreciated that tension of the wires 1 can be adjusted inall instances so as to compensate for volume changes due to shrinkageand plastic flow of the concrete; such adjustment may be made eitherprior or subsequent to the hardening of the concrete layer.

The invention is not limited to such cases where the concrete terminatesat the ends of the individual beam or girder, but may be readily adaptedto composite structures having continuous layers extending over severalspans. This is illustrated in Figs. 4 and 4a. The junction point of twoadjacent beams I rests on a support S which may consist of a similarbeam transversely arranged. It will be noted that angle plates 8 havebeen omitted; instead, supporting elements I2 are xed to the upperflanges of girders I, having a, function similar to that of pins 6 inserving as a bearing for the wires 1. 'I'he wire ties 1 of adjacentgirders are joined together by means of a turnbuckle I3 which can alsobe used to provide adequate tension, in a manner analogous to that ofscrews I1. As before, if the structure is not to be prestressed, the

wires 1 must be coated or sheathed and will receive their tension fromthe loads. The portion of the wires extending between the supportingelements I2 constitutes the negative tension flange; a compressionflange may be provided beneath the ends of adjacent girders I, e. g. bya concrete layer I4 cast between the girder flanges, if the latter arenot strong enough or not adequately connected to transfer compression.

In many instances, as in the case-of roof purlins, it will not beconvenient to support the structure at intermediate points duringhardening of the concrete. The remaining figures illustrate a method oferecting the aforedescribed composite sections under such conditions.This method consists in providing a load or reaction, temporary orotherwise, to counteract the increasing pull of the wires duringconcreting. If the wires are to be prestressed, the reaction must beprovided even before the dead load is on the .structure. If the reactionis to be temporary, it will be removed after the concrete has hardened,resulting in a transfer of the stress to the concrete layer.

A temporary load or reaction is illustrated in Fig. 5 and again, on alarger scale, in Figs. 7 and 7a. It consists of a round bar or tube I8,projecting through the bore I9 of brackets I 9a and bearing with itsends against removable plates 23 that span the slotted or recessed angleplates I5. This bar I8 should be coated or sheathed to permit itsremoval after the surrounding concrete has set. Before the concrete ispoured, or before the hardening process is completed, the wire tie 1 isadjusted to the desired stress, thus imparting compression to the memberI8 which will act as a reaction in substitution for the concrete slab.After the bar I8 has been withdrawn, the plates 23 may be reinserted tohelp transfer the stress of the wires I to the concrete layer 2.

In Fig. 5a, the temporary reaction is formed by tension means. A tensionmember is provided between brackets 20a mounted on the lower flange ofthe girder I, and the applied tension is adjusted by turnbuckle 2| untilthe desired load can be carried without undue deflection.

A permanent reaction is shown in Figs. 6 and 6a, consisting of a row ofpre-cast blocks 24 which are disposed along the girder Il between sideplates which also serve to support the ends of pins E. The blocks 24.arescored or indented `on their surfaces and are provided with recesses 22,for mechanical engagement with the concrete that is subsequently pouredover them. This concrete may form an arched layer II similar to the oneshown in Figs. 3 and 3a. An effective bond will result if the blocks 24are thoroughly wetted before the layer II is cast.

Alternatively to pre-cast blocks 24', the permanent reaction or loadproducing member may consist of a horizontal column of wood, plywood,asbestos bricks, hollow tiles, or the like. If precast concrete is used,it may have a strength of 8,000 to 10,000 p. s. i. Since this reactionmember will be permanently embodied in the concrete slab or arch, theproportions of the compressive force which will be respectively absorbedby that member and by the concrete layer will be a function of theare-as and of the moduli of elasticity, comparab'y to a reinforcedconcrete column.

It is to be understood that the invention is not to be construed aslimited to the embodiments described, and that it is on the contrarycapable of numerous adaptations and modifications without departing fromits scope as defined in the appended claims.

What is claimed is:

1. A composite metal and concrete structure, comprising a concretelayer, a metallic support having a substantially fiat, horizontalbearing surface, said layer resting on said bearing surface, at leastone metallic tie member extending underneath said layer andlongitudinally of said support, anchor means bearing endwise on saidlayer, said anchor means being in engagement with respective ends ofsaid tie member and keeping the latter under tension, thereby applyingpressure from said tie member to said layer, and bracing means securedto an intermediate portion of said supportand engaged by said tiemember, said bracing means applying a generally upward acting force tosaid portion.

2. -A composite mtal and concrete structure, comprising a concrete slab,a metallic shape having a, substantially horizontal flange supportingsaid slab and a substantially vertical web holding up said flange, aplurality of substantially horizontal projections extending from saidweb at points spaced longitudinally of said shape, anchor plates bearingon the ends of said slab, and a pair of wires under tensioninterconnecting said anchor plates and extending underneath said slab atopposite sides of said web, thereby exerting pressure upon said slab,said wires engaging said projections and applying a generally uplwardforce to said shape at said longitudinally spaced points.

3. A structure according to claim 2, wherein said horizontal flange hasa knurled surface cooperating mechanically with saidconcrete slab.

4. A structure according to claim 2, wherein said projections comprisepins extending through said web and projecting from both sides thereof.

5. A composite metal and concrete structure. comprising a plurality oflongitudinally adjacent metal beams each having a substantially flat,horizontal bearing surface, a concrete layer resting on all of saidbearing surfaces, bracing means fastened at intervals to said beams,supporting elements mounted on either side of the junction point ofadjoining beams, wire means bridging the junction between adjoiningbeams, said wire means extending underneath said bracing means andpassing through the concrete layer above said supporting elements,anchor means securing the ends of said wire means to the structure, andtensioning means maintaining said Wire means under tension, therebytending to raise portions of said structure adjacent said bracing meansrelative to said supporting elements. 6. A structure according to claim5, wherein a portion of said layer extending above the junction point ofadjacent beams surrounds part of said wire means, said wire means beingadapted to slide freely in said portion of said layer.

7. A structure according to claim 6, further comprising sheathing meansembedded in said portion of said layer and surrounding said wire neansto facilitate sliding movement of the lat- 8. A structure according toclaim 5, wherein said tensioning means include at least one turnbuckleinserted in said wire means intermediate two of said supportingelements, said wire means being adapted to slide freely in the vconcretelayer above said elements.

9. A method of erecting composite metal and concrete structures whereina layer of concrete is supported by a metallic shape, comprising thesteps of horizontally supporting said metallic shape, subjecting saidshape to upward deflection by stressing same, pouring said layer,allowing said layer to harden, anchoring an elastic tie member undertension endwise to said hardened layer, and supporting at least oneintermediate point of said shape on said tie member to counteract theweight of said layer.

10. A method according to claim 9, wherein the step of stressing saidshape includes arranging a substantially non-compressible columnlongitudinally of said shape, anchoring said tie transferred from saidcolumn to said layer after 5 the latter has hardened.

11. A method according to claim 10, further comprising the step ofremoving said column after said layer has hardened.

12. A method according to claim 9, wherein the step of stressing saidshape includes placing the lower face of a said shape under compressionby a temporary force before the layer is poured, and releasing thetemporary force effecting said compression after the layer has hardened.

LEO COFF.

REFERENCES CITED The following references are of record in the ille ofthis patent:

UNITED STATES PATENTS Number Name Date 520,491 McCarthy AMay 29, 1894960,305 Gilbreth June 7, 1910 1,000,088 Haas Aug. 8, 1911 1,813,338Batel July 7, 1931 2,016,616 Schaub Oct. 8, 1935 2,153,741 Cobi Apr. 11,1939 2,382,139 Cueni Aug. 14, 1945 FOREIGN PATENTS Number Country Date464,361 Great Britain Apr. 16, 1937 117,344 Great Britain -..July 18,1918

